This invention relates to trisubstituted piperazine compounds useful as medicines. More specifically, the present invention relates to compounds represented by the formula: ##STR2## wherein R.sup.1, R.sup.2, and R.sup.3 represent a lower alkyl group, A stands for an optionally substituted phenyl group, an optionally substituted condensed polycyclic hydrocarbon group, an optionally substituted hetero-cyclic group or a styryl group represented by the formula Ar--CR.sup.4 .dbd.CR.sup.5 -- wherein Ar stands for an optionally substituted phenyl group, and R.sup.4 and R.sup.5 respectively stand for hydrogen or a lower alkyl group, X stands for a methylene group, carbonyl group or thiocarbonyl group, and G stands for a group represented by the formula: --CH.sub.2 --.sub.n Z--R.sup.6 wherein n denotes an integer of 0 to 2, Z stands for a chemical bond, O, S, SO, SO.sub.2, CO, COO, OCO, OCONR.sup.7, CONR.sup.7 or NR.sup.7 (wherein R.sup.7 stands for hydrogen, a lower alkyl group, a lower haloalkyl group, a lower alkenyl group or a lower alkoxycarbonyl group), and R.sup.6 stands for hydrogen, a lower alkyl group, a lower haloalkyl group, a lower alkenyl group, a lower alkynyl group or a lower cycloalkyl group, provided that, when n=O and Z=chemical bond, R.sup.6 is not hydrogen or a lower alkyl group and pharmaceutically acceptable salts thereof. The compounds are useful as platelet activating factor (PAF) antagonists.
PAF has a phospholipid structure and is a chemical transmitter existing in a living body. It has been made clear that PAF is closely concerned with allergy, anaphylaxis, inflammation, etc. and it has also been known that PAF has a strong hypotensive activity and platelet agglutinating activity. On administering PAF to an animal, the animal may in some cases be killed from shock. Symptoms caused by the shock from PAF have much resemblance to those caused by the shock from endotoxin, and it has been considered that PAF is concerned with the endotoxin shock.
On the other hand, while a variety of compounds having PAF-antagonistic activity have been known, very few of them are satisfactory in PAF-antagonistic activity in a living body. And, even when the PAF-antagonistic activity in a living body is satisfactory, not a few of those compounds have some restrictions in the administration method.